Polycarbonate diol having high proportion of primary terminal oh

ABSTRACT

Disclosed is a polycarbonate diol having diol monomer units and carbonate monomer units, wherein the amount of at least one diol monomer unit selected from the group consisting of a 1,5-pentanediol unit and a 1,6-hexanediol unit is from 50 to 100% by mole, based on the total molar amount of the diol monomer units, and wherein the ratio of primary hydroxyl groups in all terminal groups of the polycarbonate diol is in a specific range. Also disclosed is a thermoplastic polyurethane obtained by copolymerizing the above-mentioned polycarbonate diol and a polyisocyanate.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a polycarbonate diol having anextremely high ratio of primary hydroxyl groups in all terminal groups.More particularly, the present invention is concerned with apolycarbonate diol having diol monomer units and carbonate monomerunits, wherein the amount of at least one diol monomer unit selectedfrom the group consisting of a 1,5-pentanediol unit and a 1,6-hexanediolunit is from 50 to 100% by mole, based on the total molar amount of thediol monomer units, and wherein the ratio of primary hydroxyl groups inall terminal groups of the polycarbonate diol is in an extremely high,specific range and, therefore, the ratio of secondary terminal hydroxylgroups is extremely low. The present invention is also concerned with athermoplastic polyurethane obtained by copolymerizing theabove-mentioned polycarbonate diol and an organic polyisocyanate.

[0003] When the polycarbonate diol of the present invention is used forproducing a thermoplastic polyurethane, a polyester elastomer and thelike, the desired polymerization reactions can proceed at high rate, ascompared to the case of the use of the conventional polycarbonate diol.Further, the thermoplastic polyurethane of the present invention hasremarkably excellent properties with respect to strength, elongation,impact resilience and low temperature properties, as compared to theproperties of a thermoplastic polyurethane obtained using theconventional polycarbonate diol.

[0004] 2. Prior Art

[0005] A polyurethane and a urethane-, ester- or amide-basedthermoplastic elastomer are used in the art. The soft segments of thepolyurethane and thermoplastic elastomer are composed of structuralunits formed from a polyester polyol and/or a polyether polyol, each ofwhich has a hydroxyl group at each of the molecular terminals thereof(for example, U.S. Pat. Nos. 4,362,825 and 4,129,715). A polyesterpolyol, such as a polyadipate polyol, has poor hydrolysis resistance.Due to the poor hydrolysis resistance, for example, a polyurethanecontaining, as soft segments, structural units formed from a polyesterpolyol has a disadvantage in that cracks are likely to occur and mold islikely to grow on the surface of the polyurethane within a relativelyshort period of time. Therefore, the use of such a polyurethane isconsiderably limited. On the other hand, a polyurethane containing, assoft segments, structural units formed from a polyether polyol has goodhydrolysis resistance. However, the polyurethane has a disadvantage inthat it has poor resistance to light and oxidative degradation. Thedisadvantages of these polyurethanes are, respectively, attributed tothe presence of ester groups in the polymer chain and the presence ofether groups in the polymer chain.

[0006] A polycarbonate polyol prepared from 1,6-hexanediol is sold as apolyol usable for forming soft segments which have excellent resistanceto hydrolysis, light, oxidative degradation, heat and the like. Thisresistance is due to the fact that carbonate linkages in the polymerchain exhibit extremely high chemical stability.

[0007] In recent years, a thermoplastic polyurethane which is producedusing, as a soft segment, a copolycarbonate diol prepared from a mixtureof 1,6-hexanediol and 1,4-butanediol or 1,5-pentanediol is attractingattention because of its great advantages. (The above-mentionedcopolycarbonate diol is disclosed in Examined Japanese PatentApplication Publication No. Hei 5-029648 (corresponding to EP 302712 andU.S. Pat. Nos. 4,855,377 and 5,070,173) and Unexamined Japanese PatentApplication Laid-Open Specification No. Hei 5-25264; and theabove-mentioned thermoplastic polyurethane is disclosed in UnexaminedJapanese Patent Application Laid-Open Specification No. Hei 5-51428 andJapanese Patent Publication No. 1985394 (corresponding to EP 302712 andU.S. Pat. Nos. 4,855,377 and 5,070,173).) Specifically, suchthermoplastic polyurethane has advantages not only in that it hasremarkably excellent properties with respect to flexibility, lowtemperature properties and elastic recovery, as well as the sameexcellent properties as mentioned above and as achieved by using, as asoft segment, a polycarbonate diol prepared from 1,6-hexanediol, butalso in that the thermoplastic polyurethane can be easily spun toproduce a polyurethane fiber.

[0008] A polycarbonate diol is produced by effecting atransesterification reaction between a diol monomer having two primaryhydroxyl groups and an organic carbonate compound, such as ethylenecarbonate, dimethyl carbonate, diethyl carbonate or diphenyl carbonate,in the presence or absence of a transesterification catalyst.

[0009] The prior art document disclosing a copolycarbonate diol preparedfrom a mixture of 1,6-hexanediol and 1,4-butanediol (Unexamined JapanesePatent Application Laid-Open Specification No. Hei 5-25264) describesthat an aliphatic polycarbonate diol containing 60 to 90% by mole ofrecurring units formed from 1,4-butanediol, based on the total molaramount of the diol monomer units, exhibits a stable reactivity in areaction thereof with a polyisocyanate for forming a polyurethane.

[0010] On the other hand, however, in the course of the studies of thepresent inventors, it was found that an aliphatic polycarbonate diol,obtained by the method of Unexamined Japanese Patent ApplicationLaid-Open Specification No. Hei 5-029648, specifically an aliphaticpolycarbonate diol containing 50% by mole or more of a recurring unitselected from the group consisting of a 1,5-pentanediol unit and a1,6-hexanediol unit, based on the total molar amount of the diol monomerunits, has the following problems. When a polyurethane-forming reactionis conducted using such an aliphatic polycarbonate diol, not only doesthe polymerization reaction rate become low, but also the resultantthermoplastic polyurethane has poor properties with respect to strength,elongation, impact resilience, low temperature properties and the like.Further, when the above-mentioned aliphatic polycarbonate diol is usedfor the production of a polyester elastomer, the polymerization reactionrate becomes low.

SUMMARY OF THE INVENTION

[0011] In this situation, the present inventors have made extensive andintensive studies with a view toward elucidating the reason why asatisfactory polymerization reaction rate cannot be obtained when aconventional polycarbonate diol is used for the production of apolyurethane or a polyester elastomer. As a result, it has unexpectedlybeen found that a polycarbonate diol contains secondary terminalhydroxyl groups derived from impurity monomers although the amount ofthese hydroxyl groups is very small, and such secondary terminalhydroxyl groups, even if the amount thereof is very small, cause alowing of the reactivity of the polycarbonate diol during apolyurethane-forming reaction and a polyester-forming reaction. Further,the present inventors have found that the problems of the prior art canbe solved by a polycarbonate diol having diol monomer units andcarbonate monomer units, wherein the amount of at least one diol monomerunit selected from the group consisting of a 1,5-pentanediol unit and a1,6-hexanediol unit is from 50 to 100% by mole, based on the total molaramount of the diol monomer units, and wherein the ratio of primaryhydroxyl groups in all terminal groups of the polycarbonate diol is inan extremely high, specific range and, therefore, the ratio of secondaryterminal hydroxyl groups is extremely low to an extent which has notever been achieved. Specifically, the present inventors have found thatsuch a polycarbonate diol having an extremely high ratio of primaryterminal hydroxyl groups exhibits high reactivity in apolyurethane-forming reaction and a polyester-forming reaction, therebyachieving high polymerization reaction rate. Also, the present inventorshave found that, when such a polycarbonate diol having an extremely highratio of primary terminal hydroxyl groups is used as a raw material forproducing a thermoplastic polyurethane, advantages are achieved not onlyin that the desired polymerization reactions can proceed at high rate,but also in that the produced thermoplastic polyurethane has remarkablyexcellent properties with respect to strength, elongation, impactresilience and low temperature properties. The present invention hasbeen completed based on these novel findings.

[0012] Accordingly, it is an object of the present invention to providea polycarbonate diol exhibiting excellent polymerization activity in areaction for producing a polyurethane and a reaction for producing apolyester elastomer.

[0013] It is another object of the present invention to provide athermoplastic polyurethane obtained by copolymerizing theabove-mentioned polycarbonate diol and a polyisocyanate, wherein thethermoplastic polyurethane can be used as various materials havingexcellent properties with respect to flexibility, heat resistance, lowtemperature properties, weathering resistance, strength, and moldingprocessability.

[0014] The foregoing and other objects, features and advantages of thepresent invention will be apparent to those skilled in the art from thefollowing detailed description and appended claims.

DETAILED DESCRIPTION OF THE INVENTION

[0015] In one aspect of the present invention, there is provided apolycarbonate diol comprising recurring units each independentlyrepresented by the following formula (1):

[0016] wherein R represents a divalent aliphatic or alicyclichydrocarbon group having 2 to 10 carbon atoms,

[0017] and terminal hydroxyl groups,

[0018] wherein 50 to 100% by mole of the recurring units of formula (1)are each independently represented by the following formula (2):

[0019] wherein n is 5 or 6, and

[0020] wherein:

[0021] when the amount of recurring units of formula (2) wherein n=5 isfrom 50 to 100% by mole, based on the total molar amount of therecurring units of formula (1), the polycarbonate diol has a primaryterminal OH ratio of 97% or more, and

[0022] when the amount of recurring units of formula (2) wherein n=5 isfrom 0 to less than 50% by mole, based on the total molar amount of therecurring units of formula (1), the polycarbonate diol has a primaryterminal OH ratio of 99% or more,

[0023] the primary terminal OH ratio being defined as the weightpercentage of diol monomers having primary hydroxyl groups at bothterminals thereof, based on the total weight of the alcohols inclusiveof diol monomers, wherein the alcohols, inclusive of diol monomers, arederived from the terminal diol segments of the polycarbonate diol andcontained in a fraction obtained by heating the polycarbonate diol at atemperature of from 160 to 200° C. under a pressure of 0.4 kPa or lesswhile stirring.

[0024] For easy understanding of the present invention, the essentialfeatures and various preferred embodiments of the present invention areenumerated below.

[0025] 1. A polycarbonate diol comprising recurring units eachindependently represented by the following formula (1):

[0026] wherein R represents a divalent aliphatic or alicyclichydrocarbon group having 2 to 10 carbon atoms,

[0027] and terminal hydroxyl groups,

[0028] wherein 50 to 100% by mole of the recurring units of formula (1)are each independently represented by the following formula (2):

[0029] wherein n is 5 or 6, and

[0030] wherein:

[0031] when the amount of recurring units of formula (2) wherein n=5 isfrom 50 to 100% by mole, based on the total molar amount of therecurring units of formula (1), the polycarbonate diol has a primaryterminal OH ratio of 97% or more, and

[0032] when the amount of recurring units of formula (2) wherein n=5 isfrom 0 to less than 50% by mole, based on the total molar amount of therecurring units of formula (1), the polycarbonate diol has a primaryterminal OH ratio of 99% or more,

[0033] the primary terminal OH ratio being defined as the weightpercentage of diol monomers having primary hydroxyl groups at bothterminals thereof, based on the total weight of the alcohols inclusiveof diol monomers, wherein the alcohols, inclusive of diol monomers, arederived from the terminal diol segments of the polycarbonate diol andcontained in a fraction obtained by heating the polycarbonate diol at atemperature of from 160 to 200° C. under a pressure of 0.4 kPa or lesswhile stirring.

[0034] 2. A polycarbonate diol according to item 1 above, wherein, whenthe polycarbonate diol is decomposed with an alkali to obtain a mixtureof diol monomers corresponding to all of the diol segments of thepolycarbonate diol, the mixture of diol monomers exhibits:

[0035] a primary hydroxyl terminal purity of 99.0% by weight or morewhen, in the polycarbonate diol, the amount of recurring units offormula (2) wherein n=5 is from 50 to 100% by mole, based on the totalmolar amount of the recurring units of formula (1), and

[0036] a primary hydroxyl terminal purity of 99.5% by weight or morewhen, in the polycarbonate diol, the amount of recurring units offormula (2) wherein n=5 is from 0 to less than 50% by mole, based on thetotal molar amount of the recurring units of formula (1),

[0037] the primary hydroxyl terminal purity being defined as the weightpercentage of the diol monomers having primary hydroxyl groups at bothterminals thereof, based on the weight of the mixture of diol monomers.

[0038] 3. A thermoplastic polyurethane obtained by copolymerizing thepolycarbonate diol of item 1 or 2 above and a polyisocyanate.

[0039] Hereinbelow, the present invention will be described in detail.

[0040] The polycarbonate diol of the present invention is apolycarbonate diol in which at least one diol monomer unit selected fromthe group consisting of a 1,5-pentanediol unit and a 1,6-hexanediol unitis present in an amount of 50% by mole or more, based on the total molaramount of the diol monomer units, wherein, when the amount of the1,5-pentanediol units is 50% by mole or more, the polycarbonate diol hasa primary terminal OH ratio of 97% or more, preferably 99% or more, andwhen the amount of the 1,5-pentanediol units is less than 50% by mole,the polycarbonate diol has a primary terminal OH ratio of 99% or more,preferably 99.4% or more, more preferably 99.6% or more. As a result ofthe extensive and intensive studies of the present inventors, it hasbeen found that the above-mentioned polycarbonate diol of the presentinvention exhibits excellent polymerization activity and highpolymerization reaction rate during a polyurethane-forming reaction andhence can be suitably used as a raw material for producing apolyurethane. Further, it has been found that the above-mentionedpolycarbonate diol also exhibits excellent polymerization activity andhigh polymerization reaction rate during a reaction for producing apolyester elastomer.

[0041] When the primary terminal OH ratio of the polycarbonate diol issmaller than the above-mentioned range required in the presentinvention, a problem arises in that, when the polycarbonate diol isreacted with a polyisocyanate in order to produce a thermoplasticpolyurethane, the polymerization reaction rate becomes markedly lowered(see Examples 5 to 10 and Comparative Examples 5 to 10, and Examples 11to 13 and Comparative Examples 11 to 13, which are described below). Itis presumed that the reason for the above-mentioned lowering of thepolymerization reaction rate resides in that the secondary terminalhydroxyl groups have a steric hindrance, which will lower theirreactivity to isocyanate groups. It should be noted that, when apolyurethane-forming reaction between such a polycarbonate diol (whichdoes not satisfy the primary terminal OH ratio requirement of thepresent invention) and a polyisocyanate is conducted for a long periodof time in order to compensate for the lowering of the polymerizationreaction rate, the produced thermoplastic polyurethane exhibits poormechanical properties (that is, a lowering of tensile strength,elongation and impact resilience occurs) (see Examples 5, 7 and 8 andComparative Examples 11 to 13, which are described below). The reasonfor the lowering of the mechanical properties of the polyurethaneproduced is considered to reside in that, due to the presence ofpolycarbonate diol chains having secondary hydroxyl terminals (whichexhibit low reactivity to isocyanate groups), during a long reactiontime, the molecular weight distribution (Mw/Mn) of the polyurethanebeing produced becomes too broad, and also the ratio of low molecularweight polyurethane molecules becomes large.

[0042] In the present invention, it is preferred that the primaryterminal OH ratio is as high as possible, because the polymerizationactivity of the polycarbonate diol is increased in accordance with anincrease in the primary terminal OH ratio of the polycarbonate diol. Forinfinitely increasing the primary terminal OH ratio of the polycarbonatediol, it is necessary to infinitely increase the purity of1,5-pentanediol and/or 1,6-hexanediol, so that too large an amount oflabor will be necessary for the purification. However, the excellenteffects of the present invention can be obtained as long as the primaryterminal OH ratio of the polycarbonate diol is not lower than the lowerlimit of the above-mentioned range required in the present invention.Therefore, there is no necessity for increasing the primary terminal OHratio to a level infinitely higher than the lower limit of theabove-mentioned range required in the present invention.

[0043] The primary terminal OH ratio referred to in the presentinvention is defined as the weight percentage of diol monomers havingprimary hydroxyl groups at both terminals thereof, based on the totalweight of the alcohols, inclusive of diol monomers, wherein thealcohols, inclusive of diol monomers, are derived from the terminal diolsegments of the polycarbonate diol and contained in a fraction obtainedby heating the polycarbonate diol at a temperature of from 160 to 200°C. under a pressure of 0.4 kPa or less while stirring.

[0044] Specifically, a polycarbonate diol (in an amount of from 70 g to100 g) is heated at a temperature of from 160 to 200° C. under apressure of 0.4 kPa or less while stirring to thereby obtain a fractionin an amount which is approximately 1 to 2% by weight of thepolycarbonate diol. That is, approximately 1 g (0.7 to 2 g) of afraction is obtained, and the obtained fraction is recovered usingapproximately 100 g (95 g to 105 g) of ethanol as a solvent, therebyobtaining a sample solution. The obtained sample solution is analyzed bygas chromatography (GC) to thereby obtain a chromatogram, and theprimary terminal OH ratio is calculated from the peak areas inaccordance with the following formula:

Primary terminal OH ratio (%)=(sum of the areas of the peaks ascribed todiol monomers having primary hydroxyl groups at both terminalsthereof)+(sum of the areas of the peaks ascribed to the alcoholsinclusive of diol monomers (but exclusive of ethanol))×100.

[0045] Specific examples of “alcohols inclusive of diol monomers (butexclusive of ethanol)” which are detected by the GC analysis performedfor determining the primary terminal OH ratio include 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,4-cyclohexanediol,1,4-pentanediol, 1-butanol, 1-pentanol, 1-hexanol and the like. A diolmonomer, such as 1,5-pentanediol or 1,6-hexanediol, used for producingthe polycarbonate diol of the present invention, is purified bydistillation in the production thereof, but an impurity alcohol having aboiling point which is close to that of the diol monomer to be purifiedwill remain in the diol monomer. However, since the boiling point ofethanol is much lower than that of a diol monomer to be purified, evenwhen ethanol is contained in a diol monomer to be purified, ethanol willbe removed from the diol monomer by the above-mentioned distillationpurification. Therefore, all of ethanol contained in the sample solutionwhich is subjected to GC for determining the primary terminal OH ratiois ascribed to the ethanol used for recovering the fraction.

[0046] The primary terminal OH ratio is the ratio of the primaryterminal OH groups in all terminal groups of the polycarbonate diol.When a polycarbonate diol is heated under the above-mentionedconditions, namely at a temperature of from 160 to 200° C. under apressure of 0.4 kPa or less while stirring, only the terminal portionsof the polycarbonate diol are decomposed to form diol monomers, and thediol monomers are distilled off and recovered as a fraction. The primaryterminal OH ratio is the weight percentage of diol monomers havingprimary hydroxyl groups at both terminals thereof, based on the totalweight of all alcohols. The higher the primary terminal OH ratio, thehigher the polymerization activity of the polycarbonate diol during apolyurethane-forming reaction and a polyester-forming reaction.

[0047] In the present invention, the lower limit of the primary terminalOH ratio is different depending on whether the amount of recurring unitsof formula (2) wherein n=5 (that is, 1,5-pentanediol-derived units) is50% by mole or more or is less than 50% by mole. The reason for this isas follows. 1,5-Pentanediol and/or 1,6-hexanediol are/is used as a rawmaterial for producing the polycarbonate diol of the present invention.Among the impurities contained in 1,6-hexanediol, an impurity containinga secondary OH group is 1,4-cyclohexanediol, and both of the two OHgroups of 1,4-cyclohexanediol are secondary OH groups. On the otherhand, among the impurities contained in 1,5-pentanediol, impuritiescontaining a secondary OH group are 1,5-hexanediol and1,4-cyclohexanediol. As mentioned above, both of the two OH groups of1,4-cyclohexanediol are secondary OH groups. However, with respect to1,5-hexanediol, one of the two OH groups thereof is a secondary OHgroup, but the other OH group thereof is a primary OH group. Therefore,when the secondary OH group of a 1,5-hexanediol molecule (an impurity)binds to a carbonate compound during the transesterification reactionfor producing a polycarbonate diol, there is a possibility that theprimary OH group of the 1,5-hexanediol molecule becomes the primaryterminal OH group of the final polycarbonate diol. In such case, noproblems will be caused by the 1,5-hexanediol molecule. The primaryterminal OH ratio is an index for evaluating the ratio of diol monomerunits formed from diol monomers having primary OH groups at bothterminals thereof in all of the diol monomer units constituting theterminal portions of the polycarbonate diol, and hence the primaryterminal OH ratio cannot be increased by the presence of 1,5-hexanediol,which has a primary terminal OH group at only one terminal thereof.Thus, when the amount of 1,5-pentanediol-derived units (1,5-pentanediolmonomer units) is 50% by mole or more (that is, when the ratio of1,5-hexanediol in the impurities contained in the raw materials ishigh), due to the presence of 1,5-hexanediol, the actual primaryterminal OH ratio of the polycarbonate diol is considered to becomeslightly higher than that determined by the above-mentioned method.Accordingly, when the amount of 1,5-pentanediol-derived units(1,5-pentanediol monomer units) is 50% by mole or more, the lower limitof the primary terminal OH ratio defined in the present invention can beslightly lower than that in the case where the amount of1,5-pentanediol-derived units (1,5-pentanediol monomer units) is lessthan 50% by mole. Based on this finding, in the present invention, thelower limit of the primary terminal OH ratio is different as between thecase where the amount of 1,5-pentanediol-derived units (1,5-pentanediolmonomer units) is 50% by mole or more and the case where the amount of1,5-pentanediol-derived units (1,5-pentanediol monomer units) is lessthan 50% by mole.

[0048] As explained above, the primary terminal OH ratio is the ratio ofthe primary OH groups in all terminal groups of the polycarbonate diol.On the other hand, the composition of all diol segments constituting thepolycarbonate diol can also be analyzed. This analysis can be made by amethod in which the polycarbonate diol is decomposed with an alkali toobtain a mixture of diol monomers corresponding to all of the diolsegments of the polycarbonate diol, and the obtained mixture is analyzedto determine the composition of all diol segments of the polycarbonatediol. Thus, a primary hydroxyl terminal purity can be determined,wherein the primary hydroxyl terminal purity is defined as the weightpercentage of the diol monomers having primary hydroxyl groups at bothterminals thereof, based on the weight of the mixture of diol monomers.It is preferred that the polycarbonate diol of the present inventionexhibits a primary hydroxyl terminal purity of 99.0% by weight or morewhen the amount of 1,5-pentanediol units in the polycarbonate diol is50% by mole or more, based on the total molar amount of the diol monomerunits. In this case, it is more preferred that the primary hydroxylterminal purity is 99.2% by weight or more, more advantageously 99.5% byweight or more. On the other hand, it is preferred that thepolycarbonate diol of the present invention exhibits a primary hydroxylterminal purity of 99.5% by weight or more when the amount of1,5-pentanediol units in the polycarbonate diol is less than 50% bymole, based on the total molar amount of the diol monomer units. In thiscase, it is more preferred that the primary hydroxyl terminal purity is99.7% by weight or more.

[0049] Exemplified below is a specific method in which a polycarbonatediol is decomposed with an alkali to obtain a diol monomer mixture,followed by analysis of the diol composition thereof (that is, followedby determination of a primary hydroxyl terminal purity of the diolmonomer mixture obtained by the decomposition of the polycarbonate diolwith an alkali). Ethanol and potassium hydroxide are added to apolycarbonate diol and heated for 1 hour in a water bath at 100° C.,thereby obtaining a reaction mixture. The obtained reaction mixture iscooled to room temperature and then neutralized using hydrochloric acid.The resultant neutralized solution is analyzed by gas chromatography(GC). It is possible that calculation of a precise weight percentage isdifficult, because in some cases not all peaks ascribed to thepolycarbonate diol can be identified by the GC analysis. Therefore, inthe present invention, “a primary hydroxyl terminal purity of 99.0% byweight or more” means that a value calculated by the following formula,which uses data obtained by the GC analysis, is 99.0 or more: (sum ofthe areas of peaks ascribed to the diol monomers having primary hydroxylgroups at both terminals thereof)+(sum of all peak areas exclusive ofthe areas of the peaks ascribed to the solvent used for diluting asample and ascribed to the internal standard which is optionally addedto the sample)×100.

[0050] Hereinbelow, a method for producing the polycarbonate diol of thepresent invention is explained. As explained below in detail, thepolycarbonate diol can be produced by effecting a transesterificationreaction between an organic carbonate compound and at least one diolmonomer selected from the group consisting of 1,5-pentanediol and1,6-hexanediol in the presence or absence of a transesterificationcatalyst. If desired, additional diol monomer(s) may also be used inaddition to the above-mentioned at least one diol monomer.

[0051] At present, commercially produced 1,5-pentanediol contains1,5-hexanediol and 1,4-cyclohexanediol, each in an amount of 0.2 to 1%by weight. These impurities (i.e., 1,5-hexanediol and1,4-cyclohexanediol) contained in 1,5-pentanediol have secondaryhydroxyl groups and hence exhibit only low reactivity during atransesterification reaction for producing a polycarbonate diol.Therefore, when a polycarbonate diol is produced using 1,5-pentanediolas a raw material, the impurities (exhibiting low reactivity) are likelyto form the terminal groups of the polycarbonate diol. As a result, theproduced polycarbonate diol contains polycarbonate diol chains havingsecondary hydroxyl groups at the terminals thereof. Such a polycarbonatediol causes a lowering of the polymerization reaction rate of apolyurethane-forming reaction. Also, such a polycarbonate diol adverselyaffects the rate of a polymerization reaction for producing a polyesterelastomer.

[0052] The purity of 1,5-pentanediol is preferably not less than 99.0%by weight, more preferably not less than 99.5% by weight. The purity of1,5-pentanediol can be determined by gas chromatography (GC).

[0053] As mentioned above, 1,5-pentanediol is likely to contain impuritydiols having a secondary hydroxyl groups. The total amount of diolmonomers having secondary hydroxyl groups is preferably less than 0.5%by weight, more preferably less than 0.3% by weight, based on the weightof 1,5-pentanediol. 1,5-Pentanediol may contain other diol monomershaving primary hydroxyl groups at both terminals thereof (for example,1,3-propanediol, 1,4-butanediol, 1,9-nonanediol,3-methyl-1,5-pentanediol, 1,4-cyclohexanedimethanol). Further,1,5-pentanediol may contain compounds which cause no adverse effects onthe synthesis of the polycarbonate diol, for example, cyclic ethersgenerated by the dehydration of 1,5-pentanediol. In addition, lactones,such as δ-valerolactone; hydroxycarboxylic acids, such as5-hydroxyvaleric acid; and monoalcohols, such as pentanol, are likely tobe by-produced during the production of 1,5-pentanediol. These compoundsmay be contained in 1,5-pentanediol, and the total content of thesecompounds in 1,5-pentanediol is preferably not more than 0.5% by weight,more preferably not more than 0.3% by weight.

[0054] 1,5-Pentanediol which is suitable for producing the polycarbonatediol of the present invention can be obtained by direct hydrogenation ofglutaric acid, using a ruthenium/tin catalyst (i.e., by hydrogenatingglutaric acid and/or an ester of glutaric acid with a lower alcohol(having 1 to 6 carbons) in the presence of a ruthenium/tin catalyst); orby hydrogenation of a glutaric acid ester, using a copper/chromiumcatalyst.

[0055] With respect to the form of glutaric acid which can be easilyobtained by a commercial process, there can be mentioned a mixture ofglutaric acid, succinic acid and adipic acid, wherein the mixture isby-produced during the production of adipic acid by subjectingcyclohexanone and/or cyclohexanol to oxidation with nitric acid. Thismixture is subjected to either a direct hydrogenation or anesterification followed by a hydrogenation, to thereby obtain a diolmonomer mixture, and the diol monomer mixture is then subjected topurification, for example, by distillation, to thereby obtain1,5-pentanediol which is suitable for producing the polycarbonate diol.

[0056] On the other hand, at present, commercially produced1,6-hexanediol contains impurities having secondary hydroxyl groups,such as 1,4-cyclohexanediol, wherein the impurities are contained in anamount of from 0.5 to 2% by weight. The impurities contained in1,6-hexanediol (such as 1,4-cyclohexanediol, which has secondaryhydroxyl groups) exhibit only low reactivity during atransesterification reaction for producing a polycarbonate diol.Therefore, when a polycarbonate diol is produced using 1,6-hexanediol asa raw material, the impurities (exhibiting low reactivity) are likely toform the terminal groups of the polycarbonate diol. As a result, theproduced polycarbonate diol contains polycarbonate diol chains havingsecondary hydroxyl groups at the terminals thereof. Such a polycarbonatediol causes a lowering of the polymerization reaction rate of apolyurethane-forming reaction, making it impossible to obtain apolyurethane having a satisfactory molecular weight. Also, such apolycarbonate diol adversely affects the rate of a polymerizationreaction for producing a polyester elastomer.

[0057] The purity of 1,6-hexanediol is preferably not less than 99.0% byweight, more preferably not less than 99.4% by weight, still morepreferably not less than 99.8% by weight. The purity of 1,6-hexanediolcan be determined by gas chromatography (GC).

[0058] The amount of 1,4-cyclohexanediol in 1,6-hexanediol is preferably0.5% by weight or less, more preferably 0.1% by weight or less, based onthe weight of 1,6-hexanediol. 1,6-Hexanediol may contain other diolmonomers having primary hydroxyl groups at both terminals thereof (forexample, 1,3-propanediol, 1,4-butanediol, 1,9-nonanediol,3-methyl-1,5-pentanediol, 1,4-cyclohexanedimethanol). Further,1,6-hexanediol may contain compounds which cause no adverse effects onthe synthesis of the polycarbonate diol, for example, cyclic ethersgenerated by the dehydration of 1,6-hexanediol. In addition, lactones,such as δ-valerolactone and ε-caprolactone; hydroxycarboxylic acids,such as 5-hydroxyvaleric acid and 6-hydroxycapronic acid; andmonoalcohols, such as pentanol and hexanol, are likely to be by-producedduring the production of 1,6-hexanediol. These compounds may becontained in 1,6-hexanediol, and the total content of these compounds in1,6-hexanediol is preferably not more than 0.5% by weight, morepreferably not more than 0.3% by weight.

[0059] 1,6-Hexanediol which is suitable for producing the polycarbonatediol of the present invention can be obtained by direct hydrogenation ofadipic acid, using a ruthenium/tin catalyst (i.e., by hydrogenatingadipic acid and/or an ester of adipic acid with a lower alcohol (having1 to 6 carbons) in the presence of a ruthenium/tin catalyst); or byhydrogenation of an adipic acid ester, using a copper/chromium catalyst.

[0060] As adipic acid which can be easily obtained by a commercialprocess, there can be mentioned adipic acid which is obtained bysubjecting cyclohexanone and/or cyclohexanol to oxidation with nitricacid in the presence of a catalyst comprising copper and vanadium tothereby form adipic acid, followed by the crystal deposition thereof.The purity of adipic acid is preferably 99.0% by weight or more, morepreferably 99.4% by weight or more, and most preferably 99.8% by weightor more. In addition, there can also be used a mixture of glutaric acid,succinic acid and adipic acid, wherein the mixture is by-produced duringthe production of adipic acid. This mixture is subjected to either adirect hydrogenation or an esterification, followed by hydrogenation, tothereby obtain a diol monomer mixture, and the diol monomer mixture isthen subjected to purification, for example, by distillation, to therebyobtain 1,6-hexanediol which is suitable for producing the polycarbonatediol.

[0061] Conventionally, 1,6-hexanediol is produced from an organic acidmixture containing adipic acid, hydroxycapronic acid and glutaric acid,wherein the organic acid mixture is by-produced during the production ofcyclohexanone and/or cyclohexanol by oxidation of cyclohexane with air.For producing 1,6-hexanediol, the organic acid mixture is subjected toesterification and then to hydrogenation in the presence of a coppercatalyst to thereby obtain 1,6-hexanediol, and the obtained1,6-hexanediol is purified by distillation. 1,6-Hexanediol which isconventionally produced in the above-mentioned manner contains1,4-cyclohexanediol, and such 1,6-hexanediol is not suitable as a rawmaterial for producing the polycarbonate diol of the present invention.The boiling point of 1,4-cyclohexanediol and the boiling point of1,6-hexanediol are very close to each other and, therefore, it isdifficult to decrease the amount of 1,4-cyclohexanediol in1,6-hexanediol to the above-mentioned preferred level (i.e., 0.5% byweight or less) by distillation.

[0062] By contrast, when 1,6-hexanediol is obtained by a method in whichadipic acid is obtained by the oxidation of cyclohexanone and/orcyclohexanol with nitric acid, and the adipic acid is subjected toeither a direct hydrogenation or an esterification followed byhydrogenation to thereby obtain 1,6-hexanediol, the obtained1,6-hexanediol has only a very small content of impurities (such as theabove-mentioned diol monomers having secondary OH groups) and hence issuitable as a raw material for producing the polycarbonate diol of thepresent invention.

[0063] Further, if desired, a diol monomer mixture containing aplurality of different types of diol monomers each having primary OHgroups at both terminals thereof can be used as a raw material forproducing the polycarbonate diol of the present invention. In such case,it is preferred that the so-called primary hydroxyl terminal purity ofthe diol monomer mixture (which has the same meaning as defined withrespect to the mixture of diol monomers obtained by the decomposition ofthe polycarbonate diol) is 99.0% by weight or more, more preferably99.5% by weigh or more, still more preferably 99.8% by weight or more.

[0064] In addition to the at least one diol monomer selected from thegroup consisting of 1,5-pentanediol and 1,6-hexanediol, if desired,other diol monomers may also be used as a raw material for producing thepolycarbonate diol of the present invention. Specific examples of suchother diol monomers include 1,3-propanediol, 1,4-butanediol,1,9-nonanediol, 3-methyl-1,5-pentanediol and 1,4-cyclohexanedimethanol.With respect to the molar ratio of 1,5-pentanediol or 1,6-hexanediol toother diol monomers, there is no particular limitation as long as thetotal amount of 1,5-pentanediol and 1,6-hexanediol is 50% by mole ormore, based on the total molar amount of all diol monomers.

[0065] In the present invention, the R groups in 50 to 100% by mole ofthe recurring units represented by formula (1) above must be comprisedof divalent groups derived from at least one diol monomer selected fromthe group consisting of 1,5-pentanediol and 1,6-hexanediol. Otherexamples of R groups in the recurring units of formula (1) includedivalent groups derived from 1,3-propanediol, 1,4-butanediol,1,9-nonanediol, 3-methyl-1,5-pentanediol and 1,4-cyclohexanedimethanol.

[0066] An especially preferred polycarbonate diol is a copolycarbonatediol synthesized from a mixture of 1,6-hexanediol and at least one diolmonomer selected from the group consisting of 1,4-butanediol and1,5-pentanediol. Such a copolycarbonate diol is preferred because athermoplastic polyurethane which is prepared using such acopolycarbonate diol exhibits excellent low temperature properties andexcellent impact resilience.

[0067] If desired, the polycarbonate diol of the present invention maybe a multifunctional polycarbonate diol which is synthesized using amixture of the above-mentioned at least one essential diol monomer(1,5-pentanediol and/or 1,6-hexanediol) and a small amount of a compoundhaving 3 or more hydroxyl groups per molecule, such astrimethylolethane, trimethylolpropane or pentaerythritol, each of whichis a polyol having primary hydroxyl groups. When polyols are used in alarge amount, the polyols are likely to form cross-linkages and causegelation. Therefore, it is preferred that the amount of the polyol isnot more than 10% by mole, based on the total molar amount of the diolmonomers.

[0068] The number average molecular weight (Mn) of the polycarbonatediol of the present invention may vary depending on the use of thepolycarbonate diol, but it is generally in the range of from 300 to50,000, preferably from 600 to 20,000. In the present invention, thenumber average molecular weight of the polycarbonate diol is determinedby the following method. The OH value of the polycarbonate diol isdetermined by the conventional neutralization titration method (JIS K0070-1992), which uses acetic acid anhydrate, pyridine and an ethanolsolution of potassium hydroxide. The number average molecular weight(Mn) is calculated from the OH value in accordance with the followingformula:

Mn=56.1×2×1,000÷OH value

[0069] As explained above, the polycarbonate diol of the presentinvention can be produced by effecting a transesterification reactionbetween an organic carbonate compound and at least one diol monomerselected from the group consisting of 1,5-pentanediol and 1,6-hexanediolin the presence or absence of a transesterification catalyst. Ifdesired, additional diol monomer(s) may also be used in addition to theabove-mentioned at least one diol monomer. Examples of organic carbonatecompounds include ethylene carbonate, dimethyl carbonate, diethylcarbonate and diphenyl carbonate.

[0070] A method for producing a polycarbonate diol without the use of acatalyst is exemplified below, wherein the method uses ethylenecarbonate as the organic carbonate compound.

[0071] The polycarbonate diol is produced by a method comprising thefollowing two steps. First, a diol monomer and ethylene carbonate aremixed together so that the molar ratio of diol monomer to ethylenecarbonate is in the range of from 20:1 to 1:10. The resultant mixture isheated at 100 to 300° C. under atmospheric or reduced pressure to effecta reaction while distilling off the by-produced ethylene glycol andunreacted ethylene carbonate, thereby obtaining a low molecular weightpolycarbonate diol having 2 to 10 diol monomer units. Subsequently, theobtained low molecular weight polycarbonate diol is subjected toself-condensation reaction at 100 to 300° C. under reduced pressurewhile distilling off the unreacted diol monomer and ethylene carbonate.The by-produced diols which are the same as the raw material diolmonomers are also distilled off during the self-condensation reaction,thereby obtaining a polycarbonate diol having a desired molecularweight.

[0072] Next, a method for producing a polycarbonate diol by using atransesterification catalyst is exemplified below.

[0073] Among the conventional, transesterification catalysts, an alkalimetal alcoholate is preferred because it can be obtained at a low costand can be easily removed from the reaction products. An alkali metalalcoholate can be removed, for example, by a reaction thereof withcarbon dioxide or by simple washing. Alternatively, an alkali metalalcoholate can be removed either by a treatment with an organic orinorganic acid or by a contact with a sulfonated acidic resin. Examplesof other catalysts which can be used for producing the polycarbonatediol of the present invention include transition metal alcoholates(which may be double salts thereof), such as Ti(OR)₄, MgTi(OR)₆, Pb(OR)₂(wherein R is an organic group), and metal oxides, such as CaO, ZnO andSnOR₂ (R is same as defined above), and a combination of thesecompounds. When, for example, diphenyl carbonate is used as an organiccarbonate, an effective amount of the catalyst is from 0.001 to 0.5% byweight, preferably 0.01% by weight, based on the weight of the reactionbulk.

[0074] The polymerization reaction is preferably performed in two stepsas in the case of the reaction performed without using a catalyst.Specifically, in step 1, a diol monomer and ethylene carbonate are mixedtogether so that the molar ratio of diol monomer to ethylene carbonateis in the range of from 20:1 to 1:10. The resultant mixture is heated at100 to 200° C. under atmospheric or reduced pressure to effect areaction while distilling off the by-produced alcohols derived from theorganic carbonate, thereby obtaining a low molecular weightpolycarbonate diol. Subsequently, in step 2, the obtained low molecularweight polycarbonate diol is heated at 150 to 300° C. under reducedpressure to effect a self-condensation reaction. The reaction isterminated when the molecular weight of the reaction product has reacheda desired value (which can be easily checked by measuring the viscosityof the reaction mixture).

[0075] When the polycarbonate diol of the present invention is used forproducing a thermoplastic polyurethane or a polyester elastomer, thedesired polymerization reactions can proceed at high rate, and thereforethe polycarbonate diol can be advantageously used as a raw material forproducing a thermoplastic polyurethane and a polyester elastomer,especially for producing a thermoplastic polyurethane.

[0076] Accordingly, the thermoplastic polyurethane of the presentinvention can be obtained by copolymerizing the polycarbonate diol ofthe present invention and a polyisocyanate.

[0077] Examples of polyisocyanates used for producing the thermoplasticpolyurethane of the present invention include conventional aromaticdiisocyanates, such as 2,4-tolylene diisocyanate, 2,6-tolylenediisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylenediisocyanate (TDI), diphenylmethane-4,4′-diisocyanate (MDI),naphthalene-1,5-diisocyanate (NDI), 3,3′-dimethyl-4,4′-biphenylenediisocyanate, crude TDI, poly-methylenepolyphenyl isocyanate, crude MDI,xylylene diisocyanate (XDI) and phenylene diisocyanate; conventionalaliphatic diisocyanates, such as 4,4′-methylene-biscyclohexyldiisocyanate (hydrogenated MDI), hexamethylene diisocyanate (HMDI),isophorone diisocyanate (IPDI) and cyclohexane diisocyanate(hydrogenated XDI); and modified products thereof, such as isocyanurateproducts, carbodimide products and biuret products.

[0078] In the present invention, if desired, a chain extender may beused as a copolymerizable component. As the chain extender, there may beemployed a customary chain extender used for producing a polyurethane,as described in, for example, “Saishin Poriuretan Oyo-Gijutsu (LatestApplication Techniques of Polyurethane)” edited by Keiji Iwata, pp.25-27, CMC, Japan, 1985. Examples of chain extenders include water, alow molecular weight polyol, a polyamine and the like. Depending on theuse of the thermoplastic polyurethane, if desired, a conventional highmolecular weight polyol may also be used in combination with thepolycarbonate diol of the present invention as long as the properties ofthe produced polyurethane are not adversely affected. As theconventional high molecular weight polyol, there may be employed thosewhich are described in, for example, pp. 12-23 of “Poriuretan Foumu(Polyurethane Foam)” by Yoshio Imai, published by Kobunshi Kankokai,Japan, 1987. Examples of high molecular weight polyols include apolyester polyol and a polyether carbonate having a polyoxyalkylenechain (i.e., a polyether carbonate polyol).

[0079] Specifically, a low molecular weight polyol used as a chainextender is generally a diol monomer having a molecular weight of notmore than 300. Examples of such low molecular weight polyols includealiphatic diols, such as ethylene glycol, 1,3-propanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol and1,10-decanediol.

[0080] Further examples of low molecular weight polyols used as a chainextender include alicyclic diols, such as 1,1-cyclohexanedimethanol,1,4-cyclohexanedimethanol and tricyclodecanedimethanol; xylylene glycol,bis(p-hydroxy)diphenyl, bis(p-hydroxyphenyl)propane,2,2-bis[4-(2-hydroxyethoxy)phenyl]propane, bis[4(2-hydroxy)phenyl]sulfone and 1,1-bis[4-(2-hydroxyethoxy)phenyl] cyclohexane. As achain extender, ethylene glycol and 1,4-butanediol are preferred.

[0081] For producing the thermoplastic polyurethane of the presentinvention, a urethane-forming technique known in the art may beemployed. For example, the polycarbonate diol of the present inventionis reacted with an organic polyisocyanate at a temperature of from roomtemperature to 200° C. to form a thermoplastic polyurethane. When achain extender is optionally used, a chain extender may be added to thereaction system either before initiating the reaction or during thereaction. For a specific method for producing a thermoplasticpolyurethane, reference can be made to U.S. Pat. No. 5,070,173.

[0082] In the polyurethane-forming reaction, a conventionalpolymerization catalyst, such as a tertiary amine and an organic salt ofa metal, e.g., tin or titanium, may be employed (see, for example,“Poriuretan Jushi (Polyurethane Resin)” written by Keiji Iwata, pages 23to 32, published in 1969 by The Nikkan Kogyo Shimbun, Ltd., Japan). Thepolyurethane-forming reaction may be performed in a solvent. Preferredexamples of solvents include dimethylformamide, diethylformamide,dimethylacetamide, dimethylsulfoxide, tetrahydrofuran, methyl isobutylketone, dioxane, cyclohexanone, benzene, toluene and ethyl cellosolve.

[0083] In the polyurethane-forming reaction, a compound having only oneactive hydrogen atom which is capable of reacting with an isocyanategroup, for example, a monohydric alcohol, such as ethyl alcohol orpropyl alcohol, and a secondary amine, such as diethylamine ordi-n-propylamine, may be used as a reaction terminator.

[0084] In the present invention, it is preferred that stabilizers, suchas heat stabilizers (for example, antioxidant) and light stabilizers,are added to the thermoplastic polyurethane.

[0085] Examples of antioxidants (heat stabilizers) include aliphatic,aromatic or alkyl-substituted aromatic esters of phosphoric acid orphosphorous acid; hypo-phosphinic acid derivatives;phosphorus-containing compounds, such as phenylphosphonic acid,phenylphosphinic acid, diphenylphosphonic acid, polyphosphonate,dialkylpentaerythritol diphosphite and a dialkylbisphenol A diphosphite;phenol derivatives, especially, hindered phenol compounds;sulfur-containing compounds, such as thioether type compounds,dithioacid salt type compounds, mercaptobenzimidazole type compounds,thiocarbanilide type compounds and thiodipropionic acid esters; andtin-containing compounds, such as tin malate and dibutyltin monooxide.

[0086] In general, antioxidants can be classified into primary,secondary and tertiary antioxidants. As hindered phenol compounds usedas a primary antioxidant, Irganox 1010 (trade name) (manufactured andsold by CIBA-GEIGY, Switzerland) and Irganox 1520 (trade name)(manufactured and sold by CIBA-GEIGY, Switzerland) are preferred. Asphosphorus-containing compounds used as a secondary antioxidant, PEP-36,PEP-24G and HP-10 (each being a trade name) (each manufactured and soldby ASAHI DENKA K.K., Japan) and Irgafos 168 (trade name) (manufacturedand sold by CIBA-GEIGY, Switzerland) are preferred. Further, assulfur-containing compounds used as a tertiary antioxidant, thioethercompounds, such as dilaurylthiopropionate (DLTP) anddistearylthiopropionate (DSTP) are preferred.

[0087] Examples of light stabilizers include UV absorber type lightstabilizers and radical scavenger type light stabilizers. Specificexamples of UV absorber type light stabilizers include benzotriazolecompounds and benzophenone compounds. Specific examples of radicalscavenger type light stabilizers include hindered amine compounds.

[0088] The above-exemplified stabilizers can be used individually or incombination. The stabilizers are added to the thermoplastic polyurethanein an amount of from 0.01 to 5 parts by weight, preferably from 0.1 to 3parts by weight, more preferably from 0.2 to 2 parts by weight, relativeto 100 parts by weight of the thermoplastic polyurethane.

[0089] If desired, a plasticizer may be added to the thermoplasticpolyurethane of the present invention. Examples of plasticizers includephthalic esters, such as dioctyl phthalate, dibutyl phthalate, diethylphthalate, butylbenzyl phthalate, di-2-ethylhexyl phthalate, diisodecylphthalate, diundecyl phthalate and diisononyl phthalate; phosphoricesters, such as tricresyl phosphate, triethyl phosphate, tributylphosphate, tri-2-ethylhexyl phosphate, trimethylhexyl phosphate,tris-chloroethyl phosphate and tris-dichloropropyl phosphate; aliphaticesters, such as octyl trimellitate, isodecyl trimellitate, trimelliticesters, dipentaerythritol esters, dioctyl adipate, dimethyl adipate,di-2-ethylhexyl azelate, dioctyl azelate, dioctyl sebacate,di-2-ethylhexyl sebacate and methylacetyl ricinoleate; pyromelliticesters, such as octyl pyromellitate; epoxy plasticizers, such asepoxidized soyabean oil, epoxidized linseed oil and epoxidized fattyacid alkyl ester; polyether plasticizers, such as adipic ether ester andpolyether; liquid rubbers, such as liquid NBR, liquid acrylic rubber andliquid polybutadiene; and non-aromatic paraffin oil.

[0090] The above-exemplified plasticizers may be used individually or incombination. The amount of the plasticizer added to the thermoplasticpolyurethane is appropriately chosen in accordance with the requiredhardness and properties of the thermoplastic polyurethane; however, ingeneral, it is preferred that the plasticizer is used in an amount offrom 0.1 to 50 parts by weight, relative to 100 parts by weight of thethermoplastic polyurethane.

[0091] In addition, other additives, such as inorganic fillers,lubricants, colorants, silicon oil, foaming agents, flame retardants andthe like, may be added to the thermoplastic polyurethane of the presentinvention. Examples of inorganic fillers include calcium carbonate,talc, magnesium hydroxide, mica, barium sulfate, silicic acid (whitecarbon), titanium oxide and carbon black. These additives may be addedto the thermoplastic polyurethane of the present invention in an amountwhich is generally used for the conventional thermoplastic polyurethane.

[0092] The Shore D hardness of the thermoplastic polyurethane of thepresent invention is preferably in the range of from 20 to 70, morepreferably from 25 to 50. When the Shore D hardness is less than 20,heat stability and scratch resistance become low. On the other hand,when the Shore D hardness is more than 70, low temperature propertiesand softness become unsatisfactory.

[0093] Further, the melt flow rate (as measured at 230° C. under a loadof 2.16 kg; hereinafter, abbreviated to “MFR”) of the thermoplasticpolyurethane of the present invention is preferably from 0.5 to 100 g/10minutes, more preferably from 5 to 50 g/10 minutes, still morepreferably from 10 to 30 g/10 minutes. When MFR is less than 0.5 g/10minutes, the injection moldability of the polyurethane becomes poor andthe injection molding is likely to result in “short shot” (that is, thefilling of the mold cavity becomes incomplete). On the other hand, whenMFR is more than 100 g/10 minutes, not only the mechanical properties(such as tensile strength and elongation at break) and abrasionresistance, but also low temperature properties are lowered.

[0094] With respect to the molecular weight of the thermoplasticpolyurethane, it is preferred that each of the number average molecularweight (Mn) and the weight average molecular weight (Mw) of thethermoplastic polyurethane is in the range of from 10,000 to 200,000.Each of Mn and Mw is measured by GPC analysis, using a calibration curveobtained with respect to standard polystyrene samples.

[0095] Hereinbelow, a method for producing a polyester elastomer byusing the polycarbonate diol of the present invention is explained. Apolyester elastomer can be produced in accordance with the various knownmethods. For example, the polycarbonate diol of the present invention, adicarboxylic ester or a combination of a dicarboxylic acid and a chainextender, and an antioxidant are charged into a reactor together with acatalyst (for example, at least one catalyst selected from the groupconsisting of tetrabutyl titanate, magnesium acetate and calciumacetate), and a reaction is effected at 100 to 250° C. under atmosphericpressure to 0.01 kPa, thereby obtaining a polyester elastomer. Withrespect to the chain extender and the antioxidant, those which areexemplified above in connection with the thermoplastic polyurethane canbe used. The antioxidant has the effect of preventing the discolorationof the polyester elastomer during the production thereof, and it ispreferred that the antioxidant is added to the polyester elastomerduring the production thereof. The use of a catalyst can decrease therequired polymerization time, thereby suppressing the heat deteriorationof the polyester elastomer during the production thereof. If desired, alight stabilizer may be added to the produced polyester elastomer. Withrespect to the light stabilizer, those which are exemplified above inconnection with the thermoplastic polyurethane can be used. As anexample of a dicarboxylic ester used for producing the polyesterelastomer, there can be mentioned dimethyl terephthalate. Representativeexamples of dicarboxylic acids used for producing the polyesterelastomer include 2,6-naphthalene dicarboxylic acid and terephthalicacid.

[0096] With respect to the molecular weight of the polyester elastomer,it is preferred that each of the number average molecular weight (Mn)and the weight average molecular weight (Mw) of the polyester elastomeris in the range of from 10,000 to 200,000. Each of Mw and Mn is measuredby GPC analysis, using a calibration curve obtained with respect tostandard polystyrene samples.

[0097] An example of a method for producing a polyester elastomer byreacting the polycarbonate diol of the present invention with adicarboxylic ester or dicarboxylic acid is as follows. The polycarbonatediol of the present invention is mixed with a dicarboxylic ester ordicarboxylic acid, and optionally added thereto is at least one memberselected from the group consisting of a chain extender, an antioxidant,a light stabilizer and a catalyst, and a polymerization reaction iseffected by heating the resultant mixture at a predetermined temperaturein a nitrogen gas atmosphere under atmospheric pressure while distillingoff the by-produced alcohol or water. The pressure of the reactionsystem is changed to reduced pressure in accordance with an increase inthe degree of polymerization of the reaction product, and if desired,the temperature is elevated to distill off the by-produced alcohol orwater and a part of the chain extender. When the degree ofpolymerization of the reaction product has reached a desired value, thepressure of the reaction system is increased to atmospheric pressure ina nitrogen gas atmosphere, and the heating is terminated, followed bycooling of the reaction system to room temperature, thereby terminatingthe reaction. With respect to the specific methods for producing apolyester elastomer, reference can be made to, for example, FrenchPatent No. 2,253,044 and Unexamined Japanese Patent ApplicationLaid-Open Specification Nos. Sho 50-40657 and Sho 50-45895.

BEST MODE FOR CARRYING OUT THE INVENTION

[0098] Hereinbelow, the present invention will be described in moredetail with reference to the following Reference Example, Examples andComparative Examples; however, they should not be construed as limitingthe scope of the present invention.

[0099] In the following Reference Example, Examples and ComparativeExamples, various measurements and analyses were conducted by thefollowing methods.

[0100] The primary terminal OH ratio of a polycarbonate diol wasmeasured by the following method. 70 g to 100 g of a polycarbonate diolwas weighed out and placed in a 300 cc eggplant shaped flask. Using arotary evaporator connected to a trap bulb for recovering a fraction,the polycarbonate diol in the eggplant shaped flask was heated in aheating bath at about 180° C. under a pressure of 0.1 kPa or less whilestirring to thereby obtain, in the trap bulb, a fraction in an amountwhich is approximately 1 to 2% by weight of the polycarbonate diol. Thatis, approximately 1 g (0.7 g to 2 g) of a fraction was obtained, and theobtained fraction was recovered using approximately 100 g (95 g to 105g) of ethanol as a solvent, thereby obtaining a sample solution. Theobtained sample solution was analyzed by gas chromatography (GC) tothereby obtain a chromatogram, and the primary terminal OH ratio wascalculated from the peak areas in accordance with the following formula:

Primary terminal OH ratio (%)=(sum of the areas of the peaks ascribed todiol monomers having primary hydroxyl groups at both terminalsthereof)÷(sum of the areas of the peaks ascribed to the alcoholsinclusive of diol monomers (but exclusive of ethanol))×100.

[0101] The analysis by GC was conducted under the following conditions.

[0102] Conditions for GC

[0103] Column: DB-WAX (column length: 30 m, film thickness: 0.25 μm)(manufactured and sold by J & W Scientific, U.S.A.)

[0104] Heating conditions: the temperature was elevated from 60° C. to250° C.

[0105] Detector: FID (flame ionization detector)

[0106] The primary hydroxyl terminal purity of a polycarbonate diol wasdetermined by the following method using an alkali decomposition.Approximately 1.0 g of a polycarbonate diol was weighed out and placedin a 100 cc eggplant shaped flask. 30 g of ethanol and 3.95 g ofpotassium hydroxide were added to the polycarbonate diol and heated for1 hour in a heating bath at about 100° C. while stirring, therebyobtaining a reaction mixture. The obtained reaction mixture was cooledto room temperature and then neutralized using hydrochloric acid. Theresultant neutralized mixture was chilled in a refrigerator for 1 hourto thereby precipitate potassium chloride formed by neutralization. Theprecipitated potassium chloride was removed by filtration and theresultant filtrate was analyzed by GC under the same conditions asmentioned above to thereby determine the weight percentage of the diolmonomers having primary hydroxyl groups at both terminals thereof, basedon the weight of the mixture of diol monomers in the filtrate.

[0107] The number average molecular weight (Mn) of the polycarbonatediol was determined by the following method. The OH value of thepolycarbonate diol was determined by the conventional neutralizationtitration method (JIS K 0070-1992), which uses acetic acid anhydrate,pyridine and an ethanol solution of potassium hydroxide. The numberaverage molecular weight (Mn) was calculated from the OH value inaccordance with the following formula:

Mn=56.1×2×1,000÷OH value.

[0108] The number average molecular weight and weight average molecularweight of a thermoplastic polyurethane were determined by GPC (gelpermeation chromatography), using a calibration curve obtained withrespect to standard polystyrene samples.

[0109] In the Examples and the Comparative Examples, various propertiesof a thermoplastic polyurethane were measured by the following methods.

[0110] (1) Shore ‘D’ Hardness [-]:

[0111] Shore ‘D’ hardness was measured in accordance with ASTM D2240, Dtype, at 23° C.

[0112] (2) Melt flow rate (MFR) [g/10 min]:

[0113] Melt flow rate was measured in accordance with ASTM D1238, undera load of 2.16 kg at 230° C.

[0114] (3) Tensile strength [kgf/cm²]:

[0115] Tensile strength was measured in accordance with JIS K6251 (usinga dumbbell No. 3 prescribed therein). A pressed sheet having a thicknessof 2 mm was used as a test sample.

[0116] (4) Elongation [%]:

[0117] Elongation was measured in accordance with JIS K6251 (using adumbbell No. 3 prescribed therein). A pressed sheet having a thicknessof 2 mm was used as a test sample.

[0118] (5) Impact resilience [%]:

[0119] Impact resilience was measured in accordance with JIS K6255(using a Lübke pendulum, 23° C.).

[0120] (6) Brittleness temperature [° C.]:

[0121] Brittleness temperature was measured in accordance with JISK6261. Specifically, the “t100 temperature” determined by the followingmethod using the Gehman torsion test was used as the brittlenesstemperature. By using a Gehman torsion tester, the torsional modulus ofa test specimen (width: 3 mm, length: 38 mm, thickness: 2 mm) wasmeasured at 23±3° C. and at various temperatures which are lower than23° C., and the ratio of the torsional modulus at each low temperatureto the torsional modulus at 23±3° C. (the ratio is hereinafter referredto as the “relative modulus”) was calculated in accordance with thefollowing formula:${RM} = {\frac{( {180 - \theta_{1}} )}{\theta_{1}}/\frac{( {180 - \theta_{0}} )}{\theta_{0}}}$

[0122] wherein,

[0123] RM: relative modulus,

[0124] θ₀: torsion angle of the test specimen at 23±3 C, and

[0125] θ₁: torsion angle of the test specimen at the low temperature.

[0126] The temperature (low temperature) at which RM (relative modulus)calculated by the formula above became 100 was defined as the “t100temperature”, and this temperature was used as the brittlenesstemperature.

REFERENCE EXAMPLE 1

[0127] <Synthesis of 1,4-butanediol, 1,5-pentanediol and 1,6-haxanediol>

[0128] An aqueous solution of a by-produced dicarboxylic acid mixturewas obtained from a commercial plant for producing adipic acid, and washeated at about 120° C. for 1 hour and, then, at a temperature of from170 to 175° C. for 30 minutes while stirring, thereby obtaining adicarboxylic acid mixture in solid form. The obtained dicarboxylic acidmixture was dissolved in ion-exchanged water to thereby obtain anaqueous dicarboxylic acid mixture solution having a dicarboxylic acidmixture content of 38% by weight. 1,000 g of the dicarboxylic acidmixture solution was contacted with 300 g of a styrene polymer typecation exchange resin (trade name: Amberlite IR-120B) (manufactured andsold by ORGANO CORP., Japan) for 2 hours, followed by removing of thecation exchange resin by filtration. The resultant filtrate (an aqueousdicarboxylic acid mixture solution) was obtained for subsequent use as araw material for the hydrogenation reaction. The dicarboxylic acidconcentration of the filtrate was 38% by weight, and the dicarboxylicacid comprised 20% by weight of succinic acid, 50% by weight of glutaricacid and 30% by weight of adipic acid.

[0129] An activated carbon (carrier) was impregnated with chloroplatinicacid hexahydrate, tin(II) chloride and ruthenium trichloride trihydrate,followed by drying of the resultant impregnated activated carbon. Then,the impregnated activated carbon was subjected to reduction treatment ina hydrogen atmosphere to thereby obtain a hydrogenation catalyst. Theobtained hydrogenation catalyst comprised an activated carbon havingcarried thereon 6.0% by weight of ruthenium, 5.0% by weight of tin and3.5% by weight of platinum. By using the hydrogenation catalyst, thehydrogenation of the above-mentioned dicarboxylic acid mixture wasperformed in the following manner.

[0130] 600 g of the above-mentioned aqueous dicarboxylic acid mixturesolution and 10 g of the above-mentioned catalyst were charged into a1,000 ml autoclave made of SUS 316. The atmosphere in the autoclave waspurged with nitrogen at room temperature and, then, pressurized hydrogengas was introduced into the autoclave to increase the internal pressurethereof to 2 MPa, and the internal temperature of the autoclave waselevated to 180° C. After the internal temperature of the autoclavereached 180° C., pressurized hydrogen gas was further introduced intothe autoclave to increase the internal pressure thereof to 15 MPa, andthen a hydrogenation reaction was performed under the above-mentionedinternal pressure for 30 hours. After completion of the hydrogenationreaction, a hydrogenation reaction mixture containing the catalyst wassubjected to filtration, to thereby recover the catalyst. The recoveredcatalyst and 600 g of the above-mentioned aqueous dicarboxylic acidmixture solution were charged into the autoclave, and a hydrogenationreaction was performed under substantially the same conditions asmentioned above. In this way, the procedure for the hydrogenation of thedicarboxylic acid mixture was repeated 9 times in total (i.e., 10 runsof the hydrogenation were performed), thereby obtaining approximately 6kg of a hydrogenation reaction mixture.

[0131] The obtained hydrogenation reaction mixture was heated to 109° C.under atmospheric pressure to distill off a large portion of watercontained in the mixture. The residual mixture was subjected todistillation using a multi-stage distillation column having 12 stages.By the distillation, water and low boiling point compounds, such aspentanol, were distilled off, thereby obtaining a purified diol monomermixture. The purified diol monomer mixture obtained was furthersubjected to distillation under reduced pressure using a multi-stagedistillation column having 35 stages. By the distillation,1,4-butanediol containing a very small amount of 1,5-pentanediol wasrecovered as a distillation fraction.

[0132] The amount of the recovered 1,4-butanediol was 342 g. Therecovered 1,4-butanediol was analyzed by gas chromatography and it wasfound that the recovered 1,4-butanediol had a purity of 99.1% by weightand contained 0.48% by weight of 1,5-pentanediol as an impurity.

[0133] A residual liquid obtained in the column bottom after thedistillation recovery of 1,4-butanediol was subjected to distillationunder reduced pressure using a multi-stage distillation column having 35stages. By the distillation, 1,5-pentanediol containing very smallamounts of 1,4-butanediol and 1,6-hexanediol was recovered as adistillation fraction.

[0134] The amount of the recovered 1,5-pentanediol was 860 g. Therecovered 1,5-pentanediol was analyzed by gas chromatography and it wasfound that the recovered 1,5-pentanediol had a purity of 99.0% by weightand contained 0.09% by weight of 1,4-butanediol, 0.29% by weight of1,6-hexanediol, not more than 0.01% by weight of 1,5-hexanediol and notmore than 0.01% by weight of 1,4-cyclohexanediol as impurities. Otherimpurities were compounds having boiling points which are higher thanthat of 1,6-hexanediol, and these other impurities could not beidentified. Accordingly, in the obtained diol monomer, which wascomposed mainly of 1,5-pentanediol, the purity of diol monomers havingprimary hydroxyl groups at both terminals thereof was 99.38% by weight,and the total content of diol monomers having a secondary hydroxyl groupwas not more than 0.02% by weight.

[0135] A residual liquid obtained in the column bottom after thedistillation recovery of 1,5-pentanediol was subjected to distillationunder reduced pressure using a multi-stage distillation column having 10stages. By the distillation, 1,6-hexanediol containing a very smallamount of 1,5-pentanediol was recovered as a distillation fraction.

[0136] The amount of the recovered 1,6-hexanediol was 476 g. Therecovered 1,6-hexanediol was analyzed by gas chromatography and it wasfound that the recovered 1,6-hexanediol had a purity of 99.1% by weightand contained 0.07% by weight of 1,4-butanediol, 0.43% by weight of1,5-pentanediol, not more than 0.01% by weight of 1,5-hexanediol and notmore than 0.01% by weight of 1,4-cyclohexanediol as impurities. Otherimpurities were compounds having boiling points which are higher thanthat of 1,6-hexanediol, and these other impurities could not beidentified.

EXAMPLE 1

[0137] 236 g (2.0 mol) of 1,6-hexanediol synthesized in ReferenceExample 1 was charged in a reaction vessel equipped with a stirrer, athermometer and a fractionating column. The 1,6-hexanediol in thereaction vessel was heated at 70° C. to 80° C., and 1.84 g (0.08 mol) ofmetallic sodium was added thereto while stirring to effect a reaction.After the metallic sodium was completely reacted, 236 g (2.0 mol) ofdiethyl carbonate was introduced into the reaction vessel, and areaction was performed under atmospheric pressure while graduallyelevating the reaction temperature up to 160° C. When the reactiontemperature was elevated to 95° C. to 100° C., ethanol began to bedistilled off. The elevation in the reaction temperature from 100° C. upto 160° C. was effected over 6 hours. During this period, a mixture ofethanol and about 10% by weight, based on the weight of the mixture, ofdiethyl carbonate was distilled off. Then, the pressure within thereaction vessel was lowered to 1.3 kPa or less and a reaction waseffected at 200° C. for 4 hours while vigorously stirring and removingdistilled ethanol from the reaction vessel. The resultant polymer wascooled, dissolved in dichloromethane and neutralized with dilute acid.The polymer was then dehydrated with anhydrous sodium sulfate. Afterremoving the solvent from the polymer by distillation, the polymer wasdried at 140° C. under 0.27 to 0.40 kPa for several hours to obtain apolycarbonate diol. The obtained polycarbonate diol of 1,6-hexanediolwas a white solid product at room temperature, and the number averagemolecular weight thereof was 2,100 and the primary terminal OH ratiothereof was 99.6%. Further, the primary hydroxyl terminal puritythereof, as measured by a method using an alkali decomposition, was99.7% by weight. Hereinafter, the obtained polymer is referred to as“pc-a”.

EXAMPLES 2 AND 3

[0138] Aliphatic copolycarbonate diols (referred to as “pc-b” and“pc-c”) were individually produced in substantially the same manner asin Example 1 except that 1,4-butanediol (abbreviated to “BDL”),1,5-petanediol (abbreviated to “PDL”) and 1,6-hexanediol (abbreviated to“HDL”), which were synthesized in Reference Example 1, were used in theamounts indicated in Table 1. The properties of the copolycarbonatediols are also shown in Table 1.

EXAMPLE 4

[0139] A polycarbonate diol (of 1,5-pentanediol) was produced insubstantially the same manner as in Example 1 except that 208 g (2.0mol) of 1,5-petanediol synthesized in Reference Example 1 was used as adiol monomer. The produced polycarbonate diol of 1,5-pentanediol was awhite solid product at room temperature, and the number averagemolecular weight thereof was 2,000 and the primary terminal OH ratiothereof was 99.2%. Further, the primary hydroxyl terminal puritythereof, as measured by a method using an alkali decomposition, was99.3% by weight.

COMPARATIVE EXAMPLES 1 TO 3

[0140] Aliphatic copolycarbonate diols (referred to as “pc-d”, “pc-e”and “pc-f”) were individually produced in substantially the same manneras in Example 1 except that commercially available diol products, namelya 1,4-butanediol product (purity determined by analysis: 98.2%), a1,5-petanediol product (purity determined by analysis: 98.5%) and a1,6-hexanediol product(purity determined by analysis: 98.6%), were usedas diol monomers in the amounts indicated in Table 1. The properties ofthe copolycarbonate diols are also shown in Table 1. TABLE 1 AmountAmount Amount Primary Primary OH terminal of BDL of PDL of HDL Numberaverage terminal purity as measured by used used used molecular weightOH ratio a method using alkali Abbreviation for (g) (g) (g) (Mn) (%)decomposition (wt %) polycarbonate diol Ex. 1 — — 236 2100 99.6 99.7pc-a Ex. 2 91 — 118 2100 99.2 99.5 pc-b Ex. 3 — 110 118 2000 99.3 99.5pc-c Compara. — — 236 2000 96.3 98.7 pc-d Ex. 1 Compara. 91 — 118 210096.5 98.6 pc-e Ex. 2 Compara. — 110 118 2000 96.0 98.3 pc-f Ex. 3

COMPARATIVE EXAMPLE 4

[0141] A commercially available 1,5-pentanediol product which isdifferent from that mentioned above in Comparative Examples 1 to 3 waspurchased and analyzed. The 1,5-pentanediol product had a purity of98.9% by weight and contained 0.62% by weight of 1,5-hexanediol and0.27% by weight of 1,4-cyclohexanediol. Further, the 1,5-pentanediolproduct contained a plurality of unidentified impurities in a totalamount of 0.21% by weight. Accordingly, the total content of diolmonomers having primary hydroxyl groups at both terminals thereof was98.9% by weight, and the total content of diol monomers having asecondary hydroxyl group was 0.89% by weight. A polycarbonate diol of1,5-pentanediol was produced in substantially the same manner as inExample 4 except that the above-mentioned commercially available1,5-pentanediol product was used as a diol monomer. The producedpolycarbonate diol was a white solid product at room temperature, andthe number average molecular weight thereof was 1,800. The primaryterminal OH ratio thereof was 96.5% and the primary hydroxyl terminalpurity thereof, as measured by a method using an alkali decomposition,was 98.9% by weight.

EXAMPLE 5

[0142] 200 g of pc-a produced in Example 1 and 67.2 g of hexamethylenediisocyanate were charged into a reaction vessel equipped with astirrer, a thermometer and a refrigeration tube. A reaction of theresultant mixture was performed at 100° C. for 4 hours while stirring,thereby obtaining a urethane prepolymer having terminal NCO groups. Tothe obtained urethane prepolymer were added 30 g of 1,4-butanediol as achain extender and 0.006 g of dibutyltin dilaurylate as a catalyst. Theresultant mixture was reacted at 140° C. for 60 minutes in a universallaboratory scale extruder (Universal Laboratory Scale Extruder KR-35type; manufactured and sold by Kasamatsu Plastic Engineering andResearch Co., Ltd., Japan) equipped with a kneader, thereby obtaining athermoplastic polyurethane. The obtained thermoplastic polyurethane wasthen pelletized using the extruder. The number average molecular weight(Mn) and weight average molecular weight (Mw) of the thermoplasticpolyurethane were, respectively, 68,000 and 146,000 as measured by GPCanalysis, using a calibration curve obtained with respect to standardpolystyrene samples. The mechanical properties of the thermoplasticpolyurethane are shown in Table 2.

EXAMPLE 6

[0143] A thermoplastic polyurethane was produced in substantially thesame manner as in Example 5 except that the amounts of pc-a,hexamethylene diisocyanate and 1,4-butanediol were changed to 200 g,24.5 g and 4.16 g, respectively. The molecular weights and mechanicalproperties of the thermoplastic polyurethane are shown in Table 2.

EXAMPLES 7 AND 8

[0144] Thermoplastic polyurethanes were produced in substantially thesame manner as in Example 5 except that pc-b and pc-c were individuallyused as a polycarbonate diol. The molecular weights and mechanicalproperties of the thermoplastic polyurethanes are shown in Table 2.

EXAMPLES 9 AND 10

[0145] Thermoplastic polyurethanes were produced in substantially thesame manner as in Example 6 except that pc-b and pc-c were individuallyused as a polycarbonate diol. The molecular weights and mechanicalproperties of the thermoplastic polyurethanes are shown in Table 2.TABLE 2 Properties of polyurethane Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10Polycarbonate diol pc-a pc-a pc-b pc-c pc-b pc-c Molecular weight numberaverage (Mn) 6.8 6.5 6.8 7.1 6.6 6.4 weight average. (Mw) 14.6 14.5 14.815.2 14.2 14.7 Mechanical properties MFR (g/10 min) 17 19 18 16 19 20Hardness (Shore D) 48 32 42 41 28 26 Tensile strength (MPa) 34 26 30 3125 26 Elongation (%) 660 700 730 760 760 790 Impact resilience (%) 38 4250 52 55 56 Brittleness temperature, −28 −30 −40 −42 −42 −44 t 100 (°C.)

COMPARATIVE EXAMPLES 5 TO 7

[0146] Thermoplastic polyurethanes were produced in substantially thesame manner as in Example 5 except that pc-d, pc-e and pc-f wereindividually used as a polycarbonate diol. The molecular weights andmechanical properties of the thermoplastic polyurethanes are shown inTable 3.

COMPARATIVE EXAMPLES 8 TO 10

[0147] Thermoplastic polyurethanes were produced in substantially thesame manner as in Example 6 except that pc-d, pc-e and pc-f wereindividually used as a polycarbonate diol. The molecular weights andmechanical properties of the thermoplastic polyurethanes are shown inTable 3. TABLE 3 Com- Com- Com- Com- Com- Com- para. para. para. para.para. para. Properties of polyurethane Ex. 5 Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex.10 Polycarbonate diol pc-d pc-e pc-f pc-d pc-e pc-f Molecular weightnumber average (Mn) 5.7 5.5 5.7 5.6 5.3 5.6 weight average. (Mw) 13.213.0 13.4 14.2 13.2 14.1 Mechanical properties MFR (g/10 min) 22 24 2524 26 28 Hardness (Shore D) 47 41 40 30 26 26 Tensile strength (MPa) 2420 22 18 15 16 Elongation (%) 450 580 620 460 620 640 Impact resilience(%) 33 46 48 36 48 50 Brittleness temperature, −25 −35 −38 −28 −38 −40 t100 (° C.)

EXAMPLE 11

[0148] 200 g of pc-a produced in Example 1 and 67.2 g of hexamethylenediisocyanate were charged into a reaction vessel equipped with astirrer, a thermometer and a refrigeration tube. A reaction of theresultant mixture was performed at 100° C. for 4 hours while stirring,thereby obtaining a urethane prepolymer having terminal NCO groups. Tothe obtained urethane prepolymer were added 30 g of 1,4-butanediol as achain extender and 0.006 g of dibutyltin dilaurylate as a catalyst. Theresultant mixture was reacted at 140° C. for 180 minutes in a universallaboratory scale extruder (Universal Laboratory Scale Extruder KR-35type; manufactured and sold by Kasamatsu Plastic Engineering andResearch Co., Ltd., Japan) equipped with a kneader, thereby obtaining athermoplastic polyurethane. The obtained thermoplastic polyurethane wasthen pelletized using the extruder. The number average molecular weight(Mn) and weight average molecular weight (Mw) of the thermoplasticpolyurethane were, respectively, 78,000 and 175,000 as measured by GPCanalysis, using a calibration curve obtained with respect to standardpolystyrene samples. The mechanical properties of the thermoplasticpolyurethane are shown in Table 4.

EXAMPLES 12 AND 13

[0149] Thermoplastic polyurethanes were produced in substantially thesame manner as in Example 11 except that pc-b and pc-c were individuallyused as a polycarbonate diol. The molecular weights and mechanicalproperties of the thermoplastic polyurethanes are shown in Table 4.

COMPARATIVE EXAMPLES 11 TO 13

[0150] Thermoplastic polyurethanes were produced in substantially thesame manner as in Example 11 except that pc-d, pc-e and pc-f wereindividually used as a polycarbonate diol. The molecular weights andmechanical properties of the thermoplastic polyurethanes are shown inTable 4. TABLE 4 Com- Com- Com- Properties of Ex. Ex. Ex. para. para.para. Polyurethane 11 12 13 Ex. 11 Ex. 12 Ex. 13 Polycarbonate diol pc-apc-b pc-c pc-d pc-e pc-f Molecular weight number average (Mn) 7.8 7.57.7 6.5 6.4 6.6 weight average (Mw) 17.5 17.3 17.7 15.8 15.5 16.3Mechanical properties MFR (g/10 min) 5.4 5.5 5.7 12 14 14 Hardness(Shore D) 48 42 41 48 42 40 Tensile strength (MPa) 38 33 35 26 24 25Elongation (%) 690 750 790 500 620 630 Impact resilience (%) 40 52 54 3546 48 Brittleness tempera- −26 −41 −42 −24 −34 −39 ture, t 100 (° C.)

INDUSTRIAL APPLICABILITY

[0151] The polycarbonate diol of the present invention exhibits highpolymerization activity in a polyurethane-forming reaction and apolyester-forming reaction. Therefore, when the polycarbonate diol ofthe present invention is used for producing a thermoplasticpolyurethane, a poly ester elastomer and the like, the desiredpolymerization reactions can proceed at high rate, as compared to thecase of the use of the conventional polycarbonate diol. Further, thethermoplastic polyurethane of the present invention has remarkablyexcellent properties with respect to strength, elongation, impactresilience and low temperature properties and hence can beadvantageously used in various application fields, such as the fields ofautomobile parts, parts for household electric appliances, toys andmiscellaneous goods. Since the thermoplastic polyurethane of the presentinvention exhibits especially improved mechanical strength, thethermoplastic polyurethane can be advantageously used in applicationfields requiring high durability, such as the fields of industrialparts, e.g., hoses, rollers and boots. The thermoplastic polyurethane isalso advantageous for use as a material for interior and exterior partsfor an automobile, such as a window mole, a bumper, a skin part for aninstrument panel and grips; wrist bands for watches and shoe soles.

1. A polycarbonate diol comprising recurring units each independentlyrepresented by the following formula (1):

wherein R represents a divalent aliphatic or alicyclic hydrocarbon grouphaving 2 to 10 carbon atoms, and terminal hydroxyl groups, wherein 50 to100% by mole of said recurring units of formula (1) are eachindependently represented by the following formula (2):

wherein n is 5 or 6, and wherein: when the amount of recurring units offormula (2) wherein n=5 is from 50 to 100% by mole, based on the totalmolar amount of said recurring units of formula (1), said polycarbonatediol has a primary terminal OH ratio of 97% or more, and when the amountof recurring units of formula (2) wherein n=5 is from 0 to less than 50%by mole, based on the total molar amount of said recurring units offormula (1), said polycarbonate diol has a primary terminal OH ratio of99% or more, said primary terminal OH ratio being defined as the weightpercentage of diol monomers having primary hydroxyl groups at bothterminals thereof, based on the total weight of the alcohols inclusiveof diol monomers, wherein said alcohols, inclusive of diol monomers, arederived from the terminal diol segments of said polycarbonate diol andare contained in a fraction obtained by heating said polycarbonate diolat a temperature of from 160 to 200° C. under a pressure of 0.4 kPa orless while stirring.
 2. A polycarbonate diol according to claim 1,wherein, when said polycarbonate diol is decomposed with an alkali toobtain a mixture of diol monomers corresponding to all of the diolsegments of said polycarbonate diol, said mixture of diol monomersexhibits: a primary hydroxyl terminal purity of 99.0% by weight or morewhen, in said polycarbonate diol, the amount of recurring units offormula (2) wherein n=5 is from 50 to 100% by mole, based on the totalmolar amount of said recurring units of formula (1), and a primaryhydroxyl terminal purity of 99.5% by weight or more when, in saidpolycarbonate diol, the amount of recurring units of formula (2) whereinn=5 is from 0 to less than 50% by mole, based on the total molar amountof said recurring units of formula (1), said primary hydroxyl terminalpurity being defined as the weight percentage of the diol monomershaving primary hydroxyl groups at both terminals thereof, based on theweight of said mixture of diol monomers.
 3. A thermoplastic polyurethaneobtained by copolymerizing the polycarbonate diol of claim 1 or 2 and apolyisocyanate.